Assessment Of The Impact Of Insecticides On Anagrus Nilapavatae (Pang Et Wang) (Hymenoptera: Mymanidae), An Egg Parasitoid Of The Rice Planthopper, Nilaparvata Lugens (Homoptera: Delphacidae)

The rice brown planthopper Nilaparvata lugens(Homoptera:delphacidae) is an important pest of rice,it is widely distributed in the rice-growing areas.The parasitoid Anagrus nilaparvatae(Pang et Wang)(Hymenoptera:mymanidae) is a major natural enemy of the rice planthopper Nilaparvata lugens,It plays an important role in the IPM of the rice planthopper.Biological control constitutes an integral part of integrated pest management strategies against N.Iugens.However,to assess its compatibility with other(chemical) management tools,insights need to be gained in possible negative effects of those on A.nilaparvatae.LC₅₀,and oral toxicity and residual effect of pesticides representing seven insecticide classes,including organophosphates,carbamates,pyrethroids,insect growth regulators(IGRs),neonicotine,phenylpyrazole,and antibiotics on mature stage of the parasitoid were investigated under laboratory conditions(sensitive).The acute and chronic effects of pesticides on A.nilaparvatae were determined. Chlorpyrifos had the highest toxicity,LO₅₀ was:0.002mg a.i./L,secondly were imidacloprid(LC₅₀:0.021 mg a.i./L) and nitenpyram(LC₅₀:0.024 mg a.i./L),but five IGRs,buprofezin,chlorfluazuron,JS118,hexaflumuron,tebufenpyrad were safest, LC₅₀ all more than 1000 mg a.i./L.Results of oral toxicity tests of 14 pesticides showed that dichlorvos was the most toxic pesticide,which generated 100%mortality only 2 hours after treatment. Isoprocarb,imidacloprid,and thiamethoxam were the second most toxic insecticides and killed all wasps in four-hour period.Imidacloprid was the most persistent insecticide,and it retained residual toxicity (80.7%mortality) on rice leaves up to 7 days after treatment.Thiamethoxam, triazophos,and fipronil also had long residual toxicity to the wasps with 7-day mortalities as 66.8%,54.6%,and 50.0%,respectively.IGRs showed very low contact and residual toxicities,but exhibited certain chronic effect of oral toxicity on longevity,oviposition,and offspring emergence.Effects of insecticides on less sensitive stage of A.nilaparvatae were tested of seven kinds of eleven insecticides.The emergence rates were not significant different when sprayed on host rice plant at different developmental stage of the parasitoids. Treatment before host parasitization,the developmental time F₀ was prolonged by fipronil,imidacloprid,dichlorvos,methamidophos and chlorpyrifos.The fecundity of F₀ was significant decreased by imidacloprid,and triazophos decreased the emergence rate of F₁ significant.Application in the mid-late larvae stage and pupae, both fipronil,imidacloprid significant reduced the adult parasitoid emergence rates.